Expression of NADPH-diaphorase and colocalization with Fos in the brain neurons of the rat following visceral noxious stimulation

We used double staining immunocytochemical techniques to determine whether nitric oxide (NO) and Fos immunoreactivity induced by noxious visceral stim ulation were colocalized in the neurons of the supraspinal areas. We observ ed a considerable increase in Foe-positive neurons in many brain areas afte r noxious stimulation but only 15% of the Fos-positive neurons colocalized Nicotinamide Adenine Dinucleotide Phosphate Diaphorase (NADPH-d). The NADPH -d positive cells showed perikarya and cytoplasmic processes laying next to or more frequently apposed to Fos-positive neurons. This anatomical findin g supported the hypothesis that also at supraspinal level NO is released ne ar the neurons specifically activated and diffuses through the source cells to act on adjacent neurons playing a role in the central processing of pai n transmission and modulation. (C) 1999 Elsevier Science B.V. All rights re served.